samarn is correct but I'm wondering if the MP4 file had been renamed. I used to have to change the suffix of files to get them to play in some players or Camtasia. E.g. 3gp to mov; mov to mp4, etc.

One way to know if it is really an MP4 file is to look at the header. One created by CS8 contains information such as "ftypmp42"; "isommp42" at the start and a bit later it contains "Mainconcept MP4 Video Media Handler".

I've noticed that all MP4 videos are not supported by Camtasia, because they've been encoded with some unsupported codec. One "simple" way to fix that is to upload the incompatible video to Youtube as a private video, and let Youtube to do the video conversion. When the conversion is ready, you can download the video from Youtube and after that it works beautifully in the Camtasia too.

I use the freemake video converter program (make sure when you install it you don't install all the bloatware, malware just choose custom install that way you don't get all that). It has a convert mp4 video to mp3 feature that use to get perfectly timed mp3 that I import to camtasia and put it just below the video with no sound.

I just wish there was a fix for this to save us some time this is obviosly a bug on codecs either from the compression program or on camtasia's side decompressor whoever's fault it is I don't really care I would love for someone to come up with a patch for this